This invention relates to the manufacture of continuous metal strips with an amorphous or polycrystalline metal structure containing embedded particulate matter by depositing molten metal containing particulate matter onto a rapidly moving surface of a chill body for forcing the metal through a slotted nozzle located in close proximity to the surface of the chill body, and more particularly to a method which effects homogeneous distribution of the particulate matter within the amorphous or polycrystalline structure.
Processes for the production of such continuous metal strips within an amorphous molecular or polycrystalline structure containing embedded particulate matter are the subject matter of U.S. Pat. Nos. 4,268,564 and 4,330,027 issuing May 19, 1981, and May 18, 1982, respectively.
In these patents, finely divided particulate matter of the type that is substantially inert, i.e. substantially chemically non-reactive with respect to the base metal under processing conditions, may be cast in the form of an amorphous metal strip containing incorporated particulate matter. By reference to FIG. 1 of the drawings, there is illustrated the apparatus performing one prior art method for the manufacture of a continuous metal strip 10 containing embedded particulate matter P on one side of the metal strip or ribbon 10. This is achieved by depositing molten metal containing a dispersed particulate matter onto the peripheral surface of a chill body 12 constituting an annular chill roll mounted for rotation about its axis by way of axle 14. A suitable reservoir 16 holds molten metal, the reservoir 16 being equipped with an electric induction coil 20 for heating the contents and also being provided with an agitator 22. In the process of the patents, when the density of the particulate matter is close to that of the melt, simple induction stirring provided by coil 20 is sufficient to maintain uniform dispersion of the particulate matter in the melt in conjunction with agitator 22. The reservoir 16 terminates at its bottom in a slotted nozzle 18 having a slot width somewhat less than the lateral width of the chill roll 12 with the nozzle orifice opening in close proximity to the surface of the chill roll 12. Means (not shown) function to pressurize the molten metal contained by reservoir 16 to effect forced expulsion thereof through the orifice of nozzle 18 onto the periphery of the rapidly rotating roll 12. In operation, molten metal containing dispersed particulate matter P, maintained under pressure in reservoir 16, is ejected through the orifice of nozzle 18 onto the peripheral surface of the rotating chill roll 12, whereupon it immediately solidifies downstream of the nozzle 18 to form strip 10.
Preferably, a nozzle such as nozzle 24 is employed to direct a stream of inert gas such as helium, argon or nitrogen against the peripheral surface of the chill roll at some point ahead of the slotted nozzle 18. By utilizing a stream of inert gas against the moving chill surface of the nozzle, it is possible to cast reactive alloys, which would burn readily when exposed to air in molten form onto the periphery of the roll 12, in the presence of an inert atmosphere, whereupon the reactive alloys harden without burning and prior to exposure to air remote from the deposition point at the orifice of nozzle 18. In many cases, in the absence of an inert gas flow such strips are insufficiently quenched and consequently have non-uniform properties and tend to be brittle. Such nozzles as nozzle 24 may also act as a "quench stabilizer" controlling the solidification process of the molten metal which leaves an immediately formed puddle after extrusion through the nozzle opening to solidify in contact with the periphery of roll 12.
In the production of such metallic strips there is a tendency as produced by the patents identified above for the particulate matter in the casting operation to tend to distribute spatially inhomogeneously in the ribbon and also to rise above the top surface of the strip being cast such that the particles protrude from that surface of the strip. Being firmly anchored within the metal matrix they function most satisfactorily within an abrasive strip with hard particles protruding from the upper surface thereof.
Under the processes of the above identified patents where the particles are added to the melt prior to forced extrusion through the nozzle orifice into contact with the quench surface of the roll (or endless belt), relatively long term contact exists between the base metal and the particles leading to adverse chemical reactions, melting of particles with lower melting points than the base metal, clumping of the particles and non-homogeneous distribution of the particles within the strip or ribbons results. Particularly in thick ribbons, particle distribution is such that periodic clumps of particles appear within the center. It is believed that the particles are rolled into the center of the vortex in the melt puddle and periodically released in vortex shedding. In the production of thin ribbons, the particles tend to segregate to the surface.
It is, therefore, a primary object of the present invention to provide an improved method of making strips of metallic glasses polycrystalline ribbons containing embedded particulate matter by pressure deposition of a stream of molten metal through an orifice of a nozzle into contact with the surface of a moving chill body to produce relatively thin strips or ribbons of metal and wherein the metal strips contain homogeneously dispersed particulate matter of the second phase particles which eliminates particle clumping and which allows high volume fraction of second phase material to be incorporated within the continuous strip of amorphous or polycrystalline metal with minimum contact time between the second phase particles and the molten base metal prior to solidification thereof.